Short-circuited winding



Patented Jan. 4, 1949 SHORT-CIRCUITED WINDING Helge Arnemo, Vasteras, Sweden, assignor to Allmanna Svenska Elektriska Akiiebolaget, Vasteras, Sweden, a corporation of Sweden Original application September 23, 1942, Serial No. 459,415. Divided and this application February 21, 1948, Serial No. 9,976. In Sweden October 19, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires October 19, 1960 1 Claim. 1

This application is a substitute for application No. 459,415 filed September 23, 1942, now abandoned.

In short circuited windings for large machines, Where the winding bars at the ends are joined by means of short-circuiting rings with large diameter, it has proved very difiicult to get a reliable connection between the bars and the short-circuiting rings. Either if this connection has been made by soldering or welding it has been approved that during service not only the connection between the bars and the ring has burst but the rupture has also continued into the ring itself. This is due to the fact that the ring under the influence of the heat generated by the current expands so much that the mechanical stress in the welding or soldering joints has reached the tensile strength. The stresses in the tangential direction will then of course be much larger than the stresses in radial direction, dependent upon the fact that in the latter direction the bars by bending can follow the deformation of the ring and in every case if the parts of the bars projecting out from the slots are not too short.

The present invention has for its object a short-circuited windin for electrical machines in order to decrease the said stresses in the joints between the short-circuiting ring and the bars of the winding. According to the invention, the bars are split at the ends and further they are fixed in the slots in one or two points dependent upon the position of the winding in relation to the air gap, so that if the winding is inside the air gap, the bars are fixed at the midst, whereas if the winding is arranged outside of the airgap, the bars are fixed in points near the ends. By the splitting up of the bars the expansion of the ring is made possible without any large stresses in tangential direction and by the said fixing only at the midst or at the ends, the bars have the possibility to be bent along their whole length when the rings expand, so that the radial stresses in the joints between the ring and the is maintained at a low value.

Instead of fixing the bars in the slots in the said manner it is sufficient, in machines where the centrifugal force on the bars is low, to arrange the bars with a small play in the slots. It is also possible to have some elastic material in 2 the slots below the bars allowing the bars to be bent along their whole length.

In the accompanying drawing, Figure 1 shows the arrangement applied on an electric coupling, in which the short-circuited winding is arranged in the outer rotating part I. The inner rotating part is designated by 2 and the winding bars by 4 and the short-circuiting rings by 3. Figure 2 is an end view of a part of the whole arrangement seen in the direction of the shaft. In this figure, AA, is the section line for the Figure l, and from this figure it is clear how the slotting 5 at the ends of the bars is performed. 6 are recesses at the upper edges of the slots, which hold the bars. These recesses are only made at the points X.

It is clear from Figure 1 that if the rings 3 expand, the bars 4 can be bent, and the central part of the bars will then move radially outwards in the slots. It is clear that the expansion of the ring in tangential direction will not give rise to any stresses to be mentioned of in the joints between the ring and the bars, because the bars are split up, so that a change of the dimensions of the ring will only cause a change of the breadth of the slots in the bars. When the bars are soldered to the ring, a sheet of mica or other suitable material is inserted in the slot in order to prevent the soldering material from filling the slot.

Figure 3 shows the application of the invention to a rotor, in which the winding is inside the air gap. In this arrangement, the bars are fixed only at the middle at the point X. It is clear that also in-this case the winding bars are free to be bent along the whole length when the ring expands.

I claim as my invention:

A device of the class described comprising in combination, a squirrel cage rotor having slots for the reception of winding bars, winding bars in said slots, respectively, and projecting beyond the ends of the rotor, means securing each bar, to the rotor, such means being intermediate the ends of the slot occupied by that bar and permitting unhampered flexing movements of the bar in a plane passing through the axis of the rotor, a short circuiting ring at each end of the rotor and concentric therewith, said rings having notches for the reception of the ends of the wind ing bars, that portion of the end of each winding REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Name Date Willis Feb. 27, 1906 Garcelon July 29, 1913 Seincke Dec. 14, 1920 McLeod et a1 July 31, 1928 FOREIGN PATENTS Country Date Great Britain Aug. 20, 1925 Great Britain Aug. 5, 1925 

